bug#20841: 25.0.50; Turning off `which-function-mode' does not remove its last effect from the minibuffer

[Stefan Kangas <stefan@marxist.se>]

tags 20841 + moreinfo unreproducible
thanks

Drew Adams <drew.adams@oracle.com> writes:

>> > Subject line says it all.
>>
>> I'm unable to reproduce this on the trunk.  I see that there have been
>> changes to the mode in the last year, but skimming the changes, I don't
>> see anything in the "switch the mode off" path...
>>
>> Are you still seeing this?
>
> Yes, I'm still seeing it.  I turn it off and I still see things
> like `[Documentation]' and `[???]' in the mode line of existing
> buffers.
>
> When this is true of *Help*, for instance, i.e., it remains
> in the mode line after I've toggled it off, if I then ask
> for something else to be displayed in *Help* (e.g. do `C-h f'),
> then it is removed from the mode line.
>
> I see this in my setup, but my setup does nothing with
> `which-function-mode'.  One guess is that the bug might
> manifest itself only if you have a standalone minibuffer.

I can't reproduce this under "emacs -Q" either.

I think we need more information here.  I suspect that this issue is
related to some package or configuration you do, possibly with regards
to the mode-line.

> Another guess might be (since ediff uses a separate control
> frame (?)) that it is similar to whatever is behind this
> comment in the code:
>
> ;; FIXME: Why does ediff require special support?

Possibly.  You could try running this to see if it makes any difference:

    (which-func-update-1 (get-buffer-window))

> Another guess is that it might have to do with
> `mode-line-misc-info'.

After my attempts reproducing the bug and reading the code, I doubt
that.  But it's possible.

> After I've turned the mode off I see that the value of
> variable `which-func-mode' remains `t' in buffers, even
> though the global value has been changed to `nil'.

That variable is t in buffers that support which-function-mode.  IOW,
this is expected.

> I don't have time to try to debug this.
> Close it if no one else has the time.  I no longer
> turn the mode on at all, to avoid the annoyance.

Maybe you have more time to investigate this today than you did when
this was first reported?

Lacking more information, I unfortunately think it will be hard to get
much further here.